1. Field of the Invention
The present invention relates to a projection display system, and more particularly, to a projection display system capable of diminishing ghost images.
2. Description of the Prior Art
The rapid development of electro-optics technologies has made projection display devices become popular both in an office and at home. A projection display device projects images on a display, in the meantime, generating some blurs, such as ghost images. Ghost images downgrade the performance of projected images and consequently become a concern to design the projection display device.
Please refer to FIG. 1, which is a projection display system 10 according to the prior art The projection display system 10 comprises an illumination system 110 and an image system 120. As far as the illumination system 110 is concerned, white light beams, emitted by a light source 111 and reflected from a reflector 112, converge onto a color generator 113, such as a color wheel. The color generator 113 comprises a series of red, green, and blue filters for transforming the white light beams into colored light beams. After leaving the color generator 113, the colored light beams sequentially pass through a light-uniform device 114, such as an integration rod or a lens array, and through an illumination lens set 115 and reach a reflection mirror 116. The reflection mirror 116 reflects the colored light beams through a field lens 117 and finally onto a light valve 121, such as a digital micro-mirror device (DMD). Reflected by the light valve 121, the colored light beams, which are projected onto the light valve 121, pass through the field lens 117 again. The colored light beams then penetrate through a projection lens 122 and project onto a screen 124, composing the image system 120.
The light valve 121, which is mounted on a substrate, is formed with a plurality of pixel lenses disposed in a matrix, each pixel lens being capable of pivotably rotating around an axis within a range of 12 degrees. The pixel lenses reflect an incident light beam onto a region inside of the projection lens 122 and the incident light beam can project onto the screen 124 when the light valve 121 is in an ON-state. The pixel lenses reflect an incident light beam onto a region outside of the projection lens 122 and, of course, outside of the screen 124 when the light valve 121 is in an OFF-state.
However, not all the colored light beams will directly project from the light valve 121 onto the screen 124. Please refer to FIG. 2A to FIG. 2C, which show light paths of ghost images of the projection display system 10 according to the prior art. As the light valve 121 is in the ON-state, the white light beams, emitted by the light source 111 will sequentially pass through the color generator 113, the light-uniform device 114, the illumination lens set 115, the reflection mirror 116, and the field lens 117, and project onto the light valve 121. The light valve 121 reflects the colored light beams onto the field lens 117 again and a first surface 1171 of the field lens 117 reflects the colored light beam back onto the light valve 121, generating second reflection colored light beams. As shown in FIG. 2A to FIG. 2C, the light valve 121 still reflects the second reflection colored light beams through the projection lens 122 and onto the screen 124, forming so-called ghost images 1241. A corresponding focal point F located on a position near the light valve 121 and corresponding to the ghost images 1241 forms a virtual ghost-image light source 1211, which is extended along a direction from the focal point F toward the light valve 121. The virtual ghost-image light source 1211 projects colors light beams onto the screen 124 to generate the ghost images 1241. The ghost images 1241 undoubtedly downgrade the performance of the projection display system 10.
Please refer to FIG. 3A to FIG. 3C, which are schematic diagrams of a first projection display system capable of diminishing ghost images according to the prior art. In the first projection display system, a convex surface with a curvature radius R less than 50 mm is formed on a first surface 1172 of the field lens 117. As the colored light beams project onto the light valve 121 and the light valve 121 reflects the colored light beams onto the field lens 117, the convex surface reflects and focuses the reflected colored light beams to a focal point F1 between the light valve 121 and the convex surface. The reflected colored light beams continue to travel toward the light valve 121 to form a light-spreading area 1212. The light valve 121 reflects the reflected colored light beams onto the screen 124 through the projection lens 122, forming spreading images 1242 and diminishing ghost images. The spreading images 1242 are not ghost images, but reduced contrast for the first projection display system.
Please refer to FIG. 4A to FIG. 4C, which are schematic diagrams of a second projection display system capable of diminishing ghost images according to the prior art. In the second projection display system, a convexo-concave surface with a curvature radius R less than 0 mm is formed on a first surface 1173 of the field lens 117. As the colored light beams project onto the light valve 121 and the light valve 121 reflects the colored light beams onto the field lens 117, the convexo-concave surface diverges the reflected colored light beams toward the light valve 121 to form a light-spreading area 1213. The light-spreading area has a virtual focal point F2. The light valve 121 reflects the reflected colored light beams onto the screen 124 through the projection lens 122, forming another spreading images 1243. The spreading images 1243 are not ghost images either, but also reduced contrast for the second projection display system.
The above-mentioned prior art projection display systems solve the ghost images problem at the cost of contrast.
It is therefore an objective of the claimed invention to provide a projection display system that can effectively diminishing ghost images.
According to the claimed invention, the projection display system includes an illumination system and an image system. The projection display system has a light source for emitting at least one light beam, and a field lens having a first surface and a second surface opposite to the first surface, the first surface having at least one reflection area. The image system utilizes the field lens and a light valve mounted adjacent to the second surface of the field lens for reflecting the light beam emitted by the light source. The light beam reflected from the light valve to the interface reflecting area is further reflected to a region outside of the light valve by the reflection area.
It is an advantage of the claimed invention that a projection display system can diminish ghost images by using the field lens with appropriate curvature radius to reflect unwanted light beams to a region outside of the light valve of the projection display system.